Self-propelling work machine and method for braking such a work machine

ABSTRACT

The invention relates to a self-propelling work machine in the form of a tracked vehicle having an electric drive, with a generator drivable by an internal combustion engine, an auxiliary unit connected to the engine, and a braking apparatus for braking the work machine. The braking apparatus provides regenerative braking by the electric drive and comprises a feedback apparatus for feeding back electrical motor braking power of the electric motor to the generator to apply the motor braking power on the engine and on the auxiliary unit. The invention further relates to a method for braking the work machine. In accordance with the invention, a control apparatus is provided for the automatic increase and/or decrease of the power pick-up of the auxiliary unit in dependence on the electrical motor braking power fed back to the engine and/or on the operating state of the engine acted on by motor braking power.

The present invention relates to a self-propelling work machine, preferably in the form of a tracked vehicle such as a bulldozer, having an electric drive comprising at least one electric motor, a generator drivable by an internal combustion engine for the supply of the electric drive with electrical energy, at least one auxiliary unit connected to the internal combustion engine as well as a braking apparatus for braking the work machine, wherein the named braking apparatus provides a regenerative braking by the electric drive and comprises a feedback apparatus for feeding back electrical motor braking power of the electric motor to the generator to apply the motor braking power on the internal combustion engine and on the auxiliary unit connected thereto. The invention further relates to a method for braking such a work machine.

With self-propelling work machines such as bulldozers or other tracked vehicles or also other self-propelling off-road vehicles for construction sites, mines and the like, electric drives having at least one electric motor have been used in recent times to utilize the typical advantages of such electric drives with respect to hydrostatic drives such as their better efficiency and an easier maintenance. Considerably lower operating costs can also be achieved at the partly substantial powers due to the substantially better efficiency. The electric drive can in this respect in particular be utilized as a traction drive by means of which at least one chain drive of the undercarriage is driven, but also for driving a main work unit such as the milling drum of a surface miner.

In this respect, a generator can be provided for the energy supply of the electric drive, said generator being drivable by an internal combustion engine, for example in the form of a diesel engine, of a gasoline engine or of a gas engine, wherein not only the power generator, but also a hydraulic unit, in particular its pump, can be driven by the internal combustion engine to be able to hydraulically drive other adjustment actuators of hydraulic components. With a bulldozer, the adjustment and/or lifting device for the trenching shovel can, for example, be driven by means of such hydraulic actuators. With dump trucks, the dump body can be rocked up and down by means of a hydraulic actuator.

A bulldozer having such a drive concept comprising an electric drive is known, for example, from U.S. Pat. No. 7,950,481, with it being proposed here to arrange an electric motor centrally and to transfer its drive power to different elements to be driven via a differential. It is proposed in this respect to store excess electrical energy which is generated by the generator with an internal combustion engine not utilized to capacity in a battery in order to be able to transfer additional electrical energy in the sense of a boost function to the electric motor when the latter requires a particularly high power, which may the case, for example, on the starting up of the machine. If, conversely, the work machine is to be braked, mechanical brakes in the form of spring pre-loaded disk brakes which can be hydraulically ventilated are actuated. Depending on the size of the work machine and on its purpose, such brakes have to be dimensioned more or less large in order not to overload or overheat on intensive braking procedures over a longer time such as can be the case with bulldozers constantly moving backward and forward or with fully loaded dump trucks traveling downhill.

U.S. Pat. No. 8,395,335 B2 furthermore describes an electric drive system for off-road trucks in which the electrical drive energy is provided by an internal combustion engine which drives a generator. In braking operation, electrical motor braking power provided by the electric motors is transferred to the generator to reduce the fuel consumption of the internal combustion engine. Excess electrical motor braking power is furthermore transferred past the internal combustion engine to electrical auxiliary units to drive these electrical units electrically and is finally dissipatively reduced or “burnt”, i.e. converted into heat, via electrical braking resistors in the form of a so-called grid box. The distribution of the electrical motor braking power, however, requires a relatively complicated control system while taking account of the electrical energy usable at the auxiliary units. In addition, the thermal load arising at the named grid box has to be taken into account.

It is the underlying object of the present invention to provide an improved work machine of the initially named kind as well as an improved method for braking such a work machine which avoid disadvantages of the prior art and further develop the latter in an advantageous manner. An energy-efficient braking with sufficient decelerations should preferably be made possible using a braking apparatus which is of a simple design and is easy to control.

The named object is achieved by a work machine in accordance with claim 1 and by a method for braking such a work machine in accordance with claim 18. Preferred embodiments of the invention are the subject of the dependent claims.

It is therefore proposed to control the braking power which can be applied on the internal combustion engine by varying the power pick-up of at least one auxiliary unit which is connected to the internal combustion engine, for example in the form of a fan, of a cooling apparatus or of a pump. In accordance with the invention, a control apparatus is provided for the automatic increase and/or decrease of the power pick-up of the at least one auxiliary unit in dependence on the electrical motor braking power fed back to the internal combustion engine and/or on the operating state of the internal combustion engine acted on by fed back motor braking power. The electrical motor braking power can in this respect be measured or determined directly by determining an electrical characteristic such as the voltage or current occurring in the feedback apparatus, for example via an inverter, or also indirectly via a characteristic accompanying the motor braking power such as a torque which the generator generates while being acted on by the fed back motor braking power. The power pick-up of the auxiliary unit can, however, not only be controlled in dependence on the motor braking power itself, but also in dependence on the operating state of the internal combustion engine acted on by the fed back motor braking power and/or on the auxiliary unit connected thereto, for example in dependence on a speed of the internal combustion engine.

Not only the regenerative motor braking power and thus also the total braking power can hereby be increased an controlled in a more variable manner and can the wear of an optionally additionally present mechanical brake be delayed, but above all an even more efficient operation of the work machine can also be achieved, for example in that a fan or a cooling apparatus is ramped up in a power respect beyond the degree required per se to cool corresponding units more than absolutely necessary so that then, with a subsequent ascent or also on a level path, the auxiliary unit can be switched off for longer or can be operated at a lower power than usual.

In a further development of the invention, it is, however, likewise possible to operate an auxiliary unit such as a pump in a dissipative manner with a higher power pick-up in order to increase the regenerative motor braking power, for example by increasing the flow rate of the pump, for example by connecting a flow resistance.

A hydraulic pump which is not required for the travel operation and which either conveys in idle circulation during driving or is swiveled to a conveying quantity of zero can in particular be used as the auxiliary unit with whose assistance the retard capacity of the retard system comprising the internal combustion engine and the auxiliary unit can be variably controlled. To increase the retard capacity of the named retard system in braking operation, the power pick-up of the hydraulic pump conveying in idle circulation during driving can advantageously be increased in that a flow resistance is successively increased in circulation. For this purpose, for example, a pre-controllable pressure-relief valve can be used which is correspondingly controlled by the control apparatus when a higher retard performance and thus a higher flow resistance is required.

If the hydraulic pump used as the auxiliary unit is swiveled to conveying a quantity of zero during driving, the power pick-up of the hydraulic pump can advantageously be increased in that the hydraulic pump is successively swiveled out in circulation against a preferably constant flow resistance, and indeed preferably against a fixedly set pressure relief valve.

Such a hydraulic pump not required in driving operation is, for example, the hydraulic pump for the pressure circuit with a bulldozer, by means of which pressure circuit the dozer blade can be adjusted.

Alternatively or additionally to such a hydraulic pump, a cooling apparatus, for example a cooling fan, can be used as the auxiliary unit whose power pick-up is adjusted which can be ramped up with a higher required braking power and which can be ramped down with a lower required braking power.

The control apparatus can in particular increase the power pick-up of at least one such auxiliary unit before an optionally present mechanical brake is used and/or further motor braking power of the at least one electric motor is dissipatively reduced, i.e. burnt, for example via a braking resistor.

The control apparatus in this respect advantageously provides that the desired braking effect is primarily achieved by regenerative braking via the electric motor(s) and the electrical motor braking power generated in thus process is applied on the internal combustion engine and on the auxiliary units connected thereto until the retard capacity of the internal combustion engine and of the auxiliary unit(s) is essentially completely exhausted.

The braking energy or the electrical motor braking power provided by the at least one electric motor is advantageously primarily fed back to the internal combustion engine when coasting via the generator which converts the electrical motor braking power into mechanical drive power for the internal combustion engine and is used there for the drive of the secondary consumers such as fans, coolers or pumps connected to the internal combustion engine and for overcoming the drag resistances of the internal combustion engine.

If the motor braking power applied on the internal combustion engine and on the auxiliary units connected thereto also exceeds a degree compatible with the internal combustion engine and the auxiliary requests after ramping up the power pick-up of the auxiliary units and/or if the internal combustion engine and/or the at least one auxiliary unit reaches a predefined operating state under the effect of the fed back motor braking power, a mechanical brake can automatically be connected or electrical energy can be transferred to the braking resistor to avoid or to reduce a further increase of the electrical motor braking power applied on the internal combustion engine. The connection of the braking resistor and/or of the mechanical brake can in this respect advantageously take place gently with—where required—successively increasing braking force so that the transition from a braking without a mechanical brake to a braking with a mechanical brake, and vice versa, takes place in the manner of a blending procedure in a gently transiting manner without a retard burst. The braking force of the mechanical brake, but also the braking power which is applied on the at least one auxiliary unit can be gently varied and controlled, in particular regulated, while taking account of the braking power already applied on the internal combustion engine, in order to come as close as possible to a desired braking force predefinable by the driver.

The electrical braking resistor can in this respect advantageously only be used briefly for the reduction of braking power peaks, for example only for some seconds, to reduce voltage peaks occurring in the voltage circuit. In permanent operation, the system can advantageously work without the named braking resistor.

Braking advantageously only takes place using the mechanical brake when the motor braking power fed back to the internal combustion engine reaches the retard capacity of the internal combustion engine and of auxiliary units which may be connected thereto.

An increasing electrical motor braking power which is generated by the at least one electric motor can in particular first be applied on the internal combustion engine with an increasing desired or required braking power, for example by increasing actuation of a brake generator and/or by an increasing slope, with the fuel supply to the internal combustion engine being successively reduced until the internal combustion engine no longer consumes any fuel at a constant speed. As the fed back electrical motor braking power increases further, the internal combustion engine can advantageously be revved up beyond a constant engine speed desired per se until a maximum permitted or maximum desired engine speed of the internal combustion engine is reached, with the named revving up of the internal combustion engine advantageously taking place with a blocked fuel supply.

If the predefined maximum speed of the internal combustion engine is reached, the control apparatus starts to ramp up the power pick-up of the at least one auxiliary unit to be able to place further motor braking power on the internal combustion engine and on the auxiliary unit connected thereto. The ramping up of the power pick-up of the auxiliary unit in this respect advantageously takes place gently in the sense of a blending procedure to ensure a gentle increase in the braking power. In this respect, the magnitude of a desired braking force is taken into account, i.e. the power pick-up of the auxiliary unit is only ramped up so much that the provided retard power is not larger than the desired retard power.

The control apparatus therefore advantageously provides a plurality of braking stages which can be connected after one another to take up the desired or required braking power. Initially or primarily, electric motor braking power is applied on the internal combustion engine without ramping up the power pick-up of the auxiliary unit or even connecting mechanical brakes to be able to operate the internal combustion engine energy efficiently with a fuel supply which is as reduced as much as possible. The power pick-up of the auxiliary unit is only ramped up in a further stage on reaching a retard capacity of the internal combustion engine or on reaching the compatibility limit of the application of the electrical motor braking power. In this respect, within the aforesaid first braking stage in which the electrical motor braking power is only or at least primarily applied on the internal combustion engine, the fuel supply is in this respect initially reduced in a first sub-stage with a substantially constant internal combustion engine speed for so long until the fuel supply is completely cut off. Once the fuel supply is cut off, a revving of the internal combustion engine is permitted in a second sub-stage.

The named control apparatus is configured in a further development of the invention such that the optionally present mechanical brakes remain unactuated or released for so long until the desired or required braking power can be applied on the internal combustion engine and on the auxiliary units connected thereto via electrical motor braking and feeding back of the motor braking power, in particular for so long until the fed back motor braking power does not exceed a predefined limit value and/or the internal combustion engine acted on by the fed back motor braking power and/or the auxiliary unit connected thereto does/do not leave a predefined operating state or operating state range, in particular does/do not exceed a predefined engine speed.

The control apparatus can in particular connect the mechanical brake in dependence on the engine speed of the internal combustion engine, and indeed in particular only when the speed of the internal combustion engine reaches a predefined maximum speed and the at least one auxiliary unit is operated to a pre-defined maximum power pick-up. The named control apparatus can for this purpose be connected to speed detection means which provided the named speed of the internal combustion engine and to determination means for determining the operating state and/or the power pick-up of the at least one auxiliary unit.

The named control apparatus can furthermore comprise engine control means for reducing the fuel supply to the internal combustion engine which initially reduce the fuel supply at a constant speed of the internal combustion engine, in particular to reduce it to an increasing degree such that with an increasing application of electrical motor braking power on the internal combustion engine the fuel supply is successively driven to zero and in so doing the engine speed is kept constant and/or at least at a predefined minimal speed, for example the idling speed.

The named control apparatus can generally be realized in different manners, for example in the form of software which is executed by a central control computer or in the form of a plurality of software modules which are executed in separate calculation modules or generally in the form of one or more separate or interlinked control modules.

The present invention will be explained in more detail in the following with reference to a preferred embodiment and to associated drawings. There are shown in the drawings:

FIG. 1: a schematic side view of a self-propelling work machine which can be configured as a bulldozer in accordance with an advantageous embodiment of the invention and which comprises an electric drive as a traction drive which is supplied with current from a generator which can be driven by an internal combustion engine, for example in the form of a diesel engine;

FIG. 2: a schematic representation of the components of the drive system of the work machine of FIG. 1 and of a control apparatus comprising a retard regulation assistant which distributes the electrical motor braking power generated on the braking of the work machine to different modules of the drivetrain and controls them; and

FIG. 3: a flowchart for presenting the method steps executed on the braking of the work machine of the previous Figures.

As FIG. 1 shows, the self-propelling work machine 1 can, for example, be configured as a bulldozer and can comprise a tracked chassis as the undercarriage 2. It is understood that the work machine can also be configured in different forms, for example as a construction machine or as a mining machine having a wheel undercarriage, for example in the form of a dump truck or truck.

The drive systems of the work machine 1 comprise at least one electric drive 3 having at least one electric motor 4 which can serve as a traction drive and can drive the chain drive of the bulldozer of FIG. 1 or a wheel of the undercarriage. As FIG. 2 shows, a plurality of electric motors 4 can also be provided, for example as an individual wheel drive or for driving a plurality of axles.

As FIG. 2 shows, the electric drive 3 is supplied with electric current from a generator 5, with the named generator 5 being driven by an internal combustion engine 6 which can be formed, for example, as a diesel engine.

The work machine 1 can furthermore comprise at least one hydraulic unit 7 which can, for example, in the embodiment of the work machine 1 in the form of a bulldozer serve for adjusting the dozer blade 8 and can for this purpose comprise at least one hydraulic actuator 9, for example in the form of a hydraulic cylinder, cf. FIG. 1.

The hydraulic unit 7 can in this respect comprise a pressure source actuable by the named internal combustion engine 6 or in the form of a hydraulic pump to supply the operating hydraulics with hydraulic fluid and hydraulic pressure.

Alternatively or additionally to the named hydraulic unit 7, the work machine 1 can also comprise further auxiliary units such as a cooling apparatus or a cooling fan which is not shown separately in the drawing and which can likewise be connected to the internal combustion engine 6.

A braking apparatus 10 for braking the work machine 1 can comprise mechanical brakes, not shown in any more detail, for braking the chain drive or the wheel drive and can be configured, for example, in the form of spring pre-loaded braking means which can be hydraulically ventilated.

The named braking apparatus 10 furthermore comprises the use of the at least one electric motor 4 as the generator in order first to provide the desired braking power by the electric drive 3 by way of regenerative braking. The electrical motor braking power provided by the electric motors 4 in thus respect is controlled and distributed by a control apparatus 11, with the named control apparatus 11 being able to comprise a feedback regulator or retard regulation assistant 12.

As FIG. 2 shows, in this respect, power electronics 13 can be associated with the electric drive 3 or with each electric motor 4, by means of which power electronics in motor operation, on the one hand, the power supplied to the electric motor 4 and, conversely, in retard operation, the returned motor braking power, can be controlled. In this respect, further power electronics 14 can also so-to-say be provided in a higher-ranking manner between the electric drive 3 and the generator 5 and can be connected to a braking resistor 15 in order optionally, where required, to be able also to reduce fed back motor braking power dissipatively at this braking resistor 15.

The aforesaid retard regulation assistant 12 is connected to the named power electronics 14 to regulate the fed back motor braking power. The named retard regulation assistant 12 is furthermore connected to the internal combustion engine 6 and to the hydraulic unit 7 in order to monitor their operating states by means of a suitable sensor system and conversely optionally also to influence their working parameters or operating parameters via control modules. A monitoring sensor system 16 can in particular comprise a speed sensor for monitoring the speed of the internal combustion engine 6 and a pressure sensor for monitoring the hydraulic pressure in the hydraulic unit 7.

In a further development of the invention, the named retard regulation assistant 12 can have engine control means 17 for controlling the internal combustion engine 6, in particular for reducing the fuel supply, and/or can have hydraulic control means 18 for controlling the hydraulic unit 7, in particular for varying the power pick-up, for example via changing the flow rate and/or the conveying pressure of the pump of the hydraulic unit 7, as previously explained.

If a machine operator desires a specific braking force, for example by actuating a brake pedal or a brake lever or by actuating a braking request button, the retard regulation assistant 12 can control or regulate the regenerative motor braking, as is illustrated in FIG. 3.

If a braking request is present the retard regulation assistant 12 first checks whether the internal combustion engine 6 is already running at its upper speed limit, cf. step 100 in FIG. 3. If this is not the case, i.e. if the internal combustion engine 6 can still provide or pick-up retard power, the retard regulation assistant 12 controls the power electronics 14 to generate regenerative motor braking power of the electric motors 4 and to feed it back to the generator 5, cf. steps 110 and 120 in FIG. 3. This feeding back of the motor braking power to the generator 5 results per se in an increase of the speed of the internal combustion engine 6, which can initially advantageously be compensated or reduced or limited in that the fuel supply is reduced, which results in a particularly efficient operation of the work machine. The fuel supply can in this respect advantageously be reduced by the retard regulation assistant such that initially no speed change of the internal combustion engine 6 occurs, with the reduction of the fuel supply being able to be increased step-wise or continuously until optionally no more fuel at all is supplied.

If such a compensation by reducing the fuel supply is no longer possible, the speed of the internal combustion engine 6 increases, which the retard regulation assistant 12 generally permits, cf. step 130 in FIG. 3.

If the motor braking power to be supplied due to the desired braking force is still smaller than the retard power which can be picked up at the internal combustion engine 6, the feedback regulation works per se in a loop, c.f. the branch 140 in the flowchart of FIG. 3. Said branch 140 is therefore taken when Pmot<Pret, i.e. the motor braking power is smaller than the retard power applied by the internal combustion engine.

If the monitoring of the speed of the internal combustion engine 6 meanwhile determines in step 130 that the internal combustion engine 6 is working at its upper speed limit, i.e. can no longer take up any further retard power, the retard regulation assistant checks in step 150 whether further motor braking power can be applied in the hydraulic unit 7, for example in that influence is taken on the conveying volume or on the conveying pressure or the pump is swiveled out further and/or a restriction resistance is increased. If the motor braking power corresponding to the desired braking force can be taken up via this, i.e. if the motor braking power does not exceed the retard power which can be provided by the internal combustion engine 6 and by the work hydraulics 7, the regulation in turn takes the branch 140.

If, on the other hand, the retard power of the hydraulic unit 7 and of optionally present further auxiliary units such as fans is reached, the retard regulation assistant 12 controls the power electronics 14 which are connected to the braking resistor 15 to dissipatively reduce further motor braking power at the named braking resistor 15, cf. steps 160 and 170 in FIG. 3. If the named braking resistor 15 cannot take up the motor braking power which cannot be applied any more at the internal combustion engine 6 and at the hydraulic unit 7, the regulation again returns via the step 140 since Pmot<Pret, cf. step 140 in FIG. 3.

If the motor braking power or the portion exceeding the retard capacity of the internal combustion engine 6 and of the hydraulic unit 7, however, exceeds the retard capacity of said braking resistor 15, the retard regulation assistant 12 reduces the motor braking power by a corresponding control of the power electronics 14, cf. step 180 in FIG. 3.

In this case, the desired braking force of the machine operator can no longer be satisfied by regenerative braking by means of the electric drive 3 so that the work machine 1 per se would be braked more slowly or less powerfully than is desired by the machine operator. To provide a remedy here, when the maximum retard power of the retard system has been reached, a mechanical brake can be connected, which can advantageously take place gently with an increasingly rising braking force to come as close as possible to a desired braking force. 

1. A self-propelling work machine having an electric drive comprising at least one electric motor; the work machine further comprising a generator drivable by an internal combustion engine and for supplying the electric drive with electrical energy, and further comprising at least one auxiliary unit connected to the internal combustion engine; the work machine further comprising a braking apparatus for braking the work machine, wherein the braking apparatus provides a regenerative braking by the electric drive and comprises a feedback apparatus for feedback of electrical motor braking power of the electric motor to the generator; wherein a control apparatus is provided for an automatic increasing and/or decreasing of power pickup of the at least one auxiliary unit in dependence on the electrical motor braking power fed back to the internal combustion engine and/or on an operating state of the internal combustion engine acted on by fed back motor braking power.
 2. The self-propelling work machine in accordance with claim 1, wherein the motor braking power of the at least one electric motor is transferred, up to a retard capacity of the internal combustion engine and of the at least one auxiliary unit, completely to the generator connected to the internal combustion engine, and mechanical drive power generated by the generator is transferred completely to the internal combustion engine; wherein the self-propelling work machine is a tracked vehicle.
 3. The self-propelling work machine in accordance with claim 1, wherein the control apparatus comprises a first braking stage wherein the electric motor braking power is applied to the internal combustion engine, wherein, in a first sub-stage, the fuel supply to the internal combustion engine is first reduced with a constant engine speed and, in a second sub-stage with a cut-off fuel supply, the speed of the internal combustion engine is increased for increasing the braking power until a predefined maximum speed is reached.
 4. The self-propelling work machine in accordance with claim 1, wherein the control apparatus is configured such that during regenerative braking the fed back motor braking power is applied to the internal combustion engine, and is further secondarily applied by increasing power pick-up of the at least one auxiliary unit when the motor braking power fed back to the internal combustion engine reaches a retard capacity of the internal combustion engine.
 5. The self-propelling work machine in accordance with claim 4, wherein the control apparatus is connectable to a speed detection device for detecting a speed of the internal combustion engine and is configured such that the power pick-up of the at least one auxiliary unit is increased on exceeding a predefined speed of the internal combustion engine and is reduced on falling below the predefined speed of the internal combustion engine.
 6. The self-propelling work machine in accordance with claim 1, wherein the control apparatus includes a regulator for regulating the power pick-up of the at least one auxiliary unit such that the internal combustion engine is maintained at a predefined speed.
 7. The self-propelling work machine in accordance with claim 1, wherein the at least one auxiliary unit is a hydraulic pump which is not required for travel operation, and conveys in idle circulation when driving or is swiveled to conveying a quantity of zero.
 8. The self-propelling work machine in accordance with claim 7, wherein the power pick-up of the hydraulic pump conveying in idle circulation when driving is increased by the control apparatus such that a flow resistance in circulation is successively increased by a pre-controllable pressure relief valve.
 9. The self-propelling work machine in accordance with claim 7, wherein the power pick-up of the hydraulic pump swiveled to conveying a quantity of zero when driving is increased by the control apparatus such that the hydraulic pump is successively swiveled out against a fixedly set pressure relief valve.
 10. The self-propelling work machine in accordance with claim 1, wherein the braking control apparatus is connected to an engine control device for controlling the fuel supply to the internal combustion engine, the engine control device configured such that during braking operation with feedback of motor braking power to the internal combustion engine, the fuel supply is reduced to maintain a constant speed of the internal combustion engine.
 11. The self-propelling work machine in accordance with claim 1, wherein the feedback apparatus comprises at least one motor inverter associated with the at least one electric motor and at least one generator inverter associated with the generator, the feedback apparatus further comprising at least one intermediate circuit between the motor inverter and the generator inverter in the form of a DC voltage intermediate circuit.
 12. The self-propelling work machine in accordance with claim 4, wherein the control apparatus is configured such that primarily the regenerative braking and only secondarily a braking by an electrical braking resistor and/or a mechanical brake takes place when the motor braking power fed back to the internal combustion engine and to the at least one auxiliary unit reaches the retard capacity of the internal combustion engine and of the at least one auxiliary unit.
 13. The self-propelling work machine in accordance with claim 12, wherein the control apparatus is configured such that the capacity of the electrical braking resistor is exhausted before connecting the mechanical brake.
 14. The self-propelling work machine in accordance with claim 12, wherein the control apparatus is configured such that the electrical braking resistor is used for reducing braking power peaks.
 15. The self-propelling work machine in accordance with claim 12, wherein the electrical braking resistor is liquid-cooled.
 16. The self-propelling work machine in accordance with claim 12, wherein the control apparatus is configured such that the electric motor braking force and/or the mechanical braking force and/or the sum of the electric motor braking force and of the mechanical braking force corresponds to a desired braking force.
 17. The self-propelling work machine in accordance with claim 1, wherein the control apparatus comprises a retard regulator for regulating the fed back motor braking power and/or for regulating the power pick-up of the at least one auxiliary unit and/or for regulating the operating state of the internal combustion engine.
 18. A method for braking a work machine having at least one electric drive comprising at least one electric motor; the work machine further comprising a generator drivable by an internal combustion engine for a power supply of the electric drive, and further comprising at least one auxiliary unit connected to the internal combustion engine; the work machine further comprising a braking apparatus, wherein the at least one electric motor is operated as a generator and a generated electrical motor braking power is fed back to the generator with a feedback apparatus, and a mechanical drive power generated by the generator is applied to the internal combustion engine; wherein a power pick-up of the at least one auxiliary unit is automatically varied by a control apparatus in dependence on the electrical motor braking power fed back to the internal combustion engine and/or on an operating state of the internal combustion engine acted on by fed back motor braking power.
 19. The method in accordance with claim 18, wherein with a small desired braking force in a first braking stage with an unchanging speed of the internal combustion engine, a fuel supply to the internal combustion engine is reduced, wherein with an increased desired braking force in a second braking stage with a cut-off fuel supply, the internal combustion engine is revved up by the fed back motor braking power up to a predefined maximum speed, and wherein with a further increased desired braking force, the power pick-up of the at least one auxiliary unit is increased in a third braking stage when the internal combustion engine has reached the predefined maximum speed.
 20. The method in accordance with claim 18, wherein the work machine is a tracked vehicle. 